1. Field of the Invention
The invention relates generally to the coexistence between a plurality of wireless communications modules, and more particularly, to systems and methods for reducing interference between a plurality of co-existed wireless communications modules.
2. Description of the Related Art
To an increasing extent, a multitude of wireless communications technologies are being merged into wireless communications devices. As shown in FIG. 1, a wireless communications device 10 may establish a wireless local area network (WLAN) via a Wireless Fidelity (WiFi) module thereof and simultaneously communicate with a Bluetooth (BT) handset through a BT module thereof. Generally, a WLAN system is implemented inside buildings as an extension to wired local area networks (LANs) and is able to provide the last few meters of connectivity between a wired network and mobile or fixed devices. According to the IEEE 802.11 standard, most WLAN systems may operate in the 2.4 GHz license-free frequency band and have very low throughput rates due to the interference from the co-located BT systems. Referring to FIG. 1, the wireless communications device 10 serves as an access point (AP) for providing WiFi communication services via the WiFi module to the WiFi stations in the established WLAN. An AP typically receives, buffers, and transmits data between the WLAN and the wired network infrastructure. The AP may support, on average, twenty WiFi stations and have a coverage varying from 20 meters in an area with obstacles (walls, stairways, elevators etc) to 100 meters in an area with clear line of sight. For example, the wireless communications device 10 may receive web-browsing data from the Internet and further transmit the data through the established WLAN to the WiFi notebook (NB) 20, and vice versa. On the other hand, BT is an open wireless protocol for exchanging data over short distances from fixed and mobile devices, creating personal area networks (PANs). The wireless communications device 10 may receive voice over the Internet protocol (VoIP) data from the Internet and then forward the VoIP data through the established PAN to the BT handset 30. Alternatively, the wireless communications device 10 may receive digital music via the WiFi module and transmit the digital music through the established PAN to be played back in the BT handset 30. Note that the WLAN and BT systems both occupy a section of the 2.4 GHz Industrial, Scientific, and Medical (ISM) band, which is 83 MHz-wide. Due to cost issues as well as space requirements for components, modern electronic devices, such as cellular phones, Ultra-Mobile PCs (UMPCs) or others, are equipped with WiFi and BT modules sharing a single antenna instead of multiple antennas.
As an example shown in FIG. 2, a BT system uses a Frequency Hopping Spread Spectrum (FHSS) and hops between 79 different 1 MHz-wide channels in a Bluetooth spectrum. A WLAN system uses a Direct Sequence Spread Spectrum (DSSS) instead of a FHSS. A WLAN system carrier remains centered on one channel, which is 22 MHz-wide. When the WiFi module and the BT module are operating simultaneously in the same area, as shown in FIG. 1, the single WLAN channel, which is 22 MHz-wide, occupies the same frequency space as 22 out of 79 BT channels which are 1 MHz-wide. When a BT transmission occurs on a frequency band that falls within the frequency space occupied by an ongoing WLAN transmission, a certain level of interference may occur, depending on the signal strength thereof. Due to the fact that the WiFi module and BT module share the same spectrum and also share a single antenna, avoiding interference therebetween is required.
FIG. 3 is a diagram illustrating operations of the WiFi module and BT module sharing a single antenna in the wireless communication device of FIG. 1. In FIG. 3, the shared single antenna is switched between WLAN and BT communication services in a given time slot for transceiving data. If the BT communication service carries audio data that requires real-time transmission, for example, the Synchronous Connection-Oriented (SCO) packets and the Asynchronous Connection-Less (ACL) packets, the BT communication service would have a higher priority over the WLAN communication service. In this case, when a WLAN transceiving process takes place at the same time as the real-time BT transceiving process, the time slot will be assigned to the BT transceiving process and the WLAN transceiving process will be blocked. As shown in FIG. 3, the WiFi receiving operation (Rx operation) 1 occurs in the time slot, while the BT communication service is idle. Therefore, the Rx operation 1 is performed without interference and an acknowledgement (ACK) message 2 is transmitted to the WiFi NB as a reply message indicating that the Rx operation 1 is finished. Following the Rx operation 1, another WiFi Rx operation 3 is performed. The Rx operation 3 is also performed without interference because the BT communication service is in the idle state. However, an ACK message 4 in response to the Rx operation 3 can not be transmitted, as the channel resources are already assigned to the BT transmitting operation (Tx operation). Accordingly, the Rx operation 3 would be determined to have failed. In response to the failure, the WiFi NB 20 would retransmit the data with a lower data rate in an attempt to successfully transmit data to the WiFi module in the wireless communications device 10. Unfavorably, the re-performed Rx operation 3 (denoted as 5), with a prolonged operation period, will be more likely to overlap with the BT transceiving process. Another data retransmitted with a lower data rate than that of the prior retransmission would be further attempted, causing more overlap with the BT transceiving process than the prior attempt. It is noted that, the channel resources of all the WiFi stations are reserved for the BT transceiving process to avoid the coexistence interference, even though the received signals from the WiFi stations located in a short distance may have enough Signal to Interference and Noise Ratio (SINR) to withstand the coexistence interference. As a result, WiFi throughput is highly hindered as the WiFi and BT modules share a single antenna.